The present invention has for its object a method for the pulse-burning of fuel gases in industrial furnaces, particularly metallurgical furnaces, for example furnaces for the heating and the thermic treating of metallurgical products and metallurgical-mechanical products, by employing a burner comprising a main combustion chamber to which there is fed in a pulsating manner a primary mix of fuel gas and air in a substantially stoichiometric ratio, and an auxiliary combustion chamber to which there is fed in a continuous manner an auxiliary mix of fuel gas and air, and the combustion products of which auxiliary chamber enter continuously into the main combustion chamber.
The method above referred to is known from the following Soviet publication: Rapport of TSNIITMASH on the theme "The chioce of thermic furnaces, test of the pulse-burners employing fuel gas," theme No. 27, 20-1235.01 etap 53, Moscow, 1978. By this method, the pulses of feeding of the primary mix of fuel gas and air to the main combustion chamber are alternated with complete interruptions of the combustion in the main chamber. At the starting of each feeding pulse, the primary mix of fuel gas and air fed the main combustion chamber, is ignited (fired) thanks to the combustion products which flow out continuously from the auxiliary combustion chamber, to which the auxiliary mix of fuel gas and air is fed in a continuous manner.
The known method presents however the inconvenience that the ignition (firing) of the primary mix of fuel gas and air inside the main combustion chamber takes place in a sudden manner and causes, particularly whenever the main combustion chamber is cold, strong pressure blows both in the said main combustion chamber and in the ducts supplying the fuel gas and the air upstream of the burner. The said pressure blows damage the refractory blocks of the main combustion chamber, by subjecting them to remarkable stresses which determine their premature breaking. Moreover, the said pressure blows cause unbalances and alterations in the pressures and in the rates of flow of the fuel gas and of the air upstream of the burner, so that the ratio between the fuel gas and the air in the primary mix fed to the main combustion chamber comes to be different, during transitional time periods, from the predetermined stoichiometric ratio, thus reducing the efficiency of the combustion. Moreover, by employing the known methods of the above mentioned type, also the instant of ignition (firing) of the primary mix of fuel gas and air in the main combustion chamber results to be imprecise and unstable and can be very much delayed.
The invention has for its object to eliminate the inconveniences of the known methods, by improving the above referred method in such a manner as to stabilize and render more gradual and precise the ignition of the primary mix of fuel gas and air inside the main combustion chamber, and to avoid strong pressure blows at the moment of the ignition thus eliminating the respective stresses on the refractory blocks and increasing their life, as well as to avoid the temporary disorder of the predetermined stoichiometric ratio between the fuel gas and the air, thus ensuring in a continuous manner the optimum efficiency of the combustion.
The above problem is solved by the present invention by employing a method of the referred type and which is characterized substantially by the fact that alternatingly to the pulses of feeding of the primary mix of fuel gas and air in substantially stoichiometric ratio, that is during the intervals between the feed pulses of the said primary mix, there is fed to the main combustion chamber a secondary mix of fuel gas and air with a coefficient of excess air of 1.15 to 1.35,preferably 1.2, and at a rate of flow corresponding to about 1 to 3%, preferably 2%, of the nominal rate of flow of the primary mix of fuel gas and air in stoichiometric ratio, while the auxiliary mix of fuel gas and air presents a coefficient of excess air of 0.65 to 0.85, preferably 0.8, and it is fed to the auxiliary combustion chamber at a rate of flow corresponding to about 1 to 3%, preferably 2%, of the nominal rate of flow of the primary mix of fuel gas and air in stoichiometric ratio.
Preferably, according to a further feature of the invention, the combustion products of the auxiliary mix of fuel gas and air stay in the auxiliary combustion chamber for such a short time that, when they enter into the main combustion chamber, they still contain active chemical substances, particularly hydrogen atoms and radicals containing hydrogen atoms.
The invention provides also for a preferred apparatus for carrying out the above mentioned method. The said apparatus comprises a main combustion chamber provided with an outlet channel and with an inlet channel, the said inlet channel being connected, by means of a mixer device for mixing the fuel gas and the air, to an adjustable feeder device operating in a pulsating manner for feeding fuel gas and air, in a ratio and at a rate of flow which can be automatically varied according to a predetermined program, swirling devices being also provided which are suitable for imparting a swirling motion to the primary mix of fuel gas and air, fed in a pulsating manner to the main combustion chamber, there being also provided an auxiliary combustion chamber comprising an electric ignition (firing) plug, said auxiliary chamber presenting a plurality of outlet channels communicating with the main combustion chamber, as well as an inlet duct connected to a continuous feeder device for feeding an auxiliary mix of fuel gas and air. According to the invention, the said apparatus is characterized by the fact that the auxiliary combustion chamber presents a volume which is such that the stay time at its interior of the combustion products of the auxiliary mix of fuel gas and air corresponds to about 0.005 to 0.01 sec.
The auxiliary combustion chamber can be constructed in various manners and, by way of example, it can be annular, cylindrical or spherical, coaxial to the main combustion chamber, while the outlet channels from the said auxiliary combustion chamber can open into the initial portion, which is generally shaped in a flaring-out manner, of the main combustion chamber, or into the inlet channel of said main chamber.
The above and other characteristic features of the invention, and the advantages deriving therefrom will appear in a more detailed manner, from the following description, made by way of non-limiting example, with reference to the annexed drawings.